Drill point screw having interrupted leading end threads formed by a flat chordal surface



b V in July 24, 1962 TH DS FOR A FL. CHORDAL SUR Fil g. 25, 60

E. REED 2ND 3,045,523 LL NT SCREW HAVING INTERRUPTED LEADING FACE INVENTOR EDGAR RE E D, 2N0.

ATTORNEYS DRILL POINT SCREW HAVING INTERRUFTED LEADING END THREADS FORMED BY A FLAT CI-IURDAL SURFACE Edgar Reed 2nd, 24 Butternut Hill Road, Worcester, Mass. Filed Aug. 25, 1960, Ser. No. 51,915 3 Claims. (Cl. 35-47) This invention relates broadly to screw fasteners and, more particularly, to screws which are constructed and intended to be driven into hard wood without a predrilled lead hole.

-It is well known that considerable and important difficulties are encountered in driving a screw into hard wood, in addition to the fact that considerable force is required to drive the screw. A principal difficulty is that the wood is split by the screw, while another difiiculty is that the screw breaks or the driving slot in the head is deformed or broken, thus preventing or rendering extremely difficult the removal or further driving of the screw. In usual practice, before this invention, these diificulties have made it necessary to form a lea-d hole into which the screw is driven.

It has accordingly been the principal object of this invention to provide a wood screw of new and improved construction which may be driven into hard wood without a lead hole and with less force than is required to drive screws of known construction into the same wood, whereby the driving slot is not broken or deformed during driving, and which will not split the wood even though driven into the hardest woodto the full length of the screw.

The invention is described in the following specification and is illustrated in the accompanying drawing, in which:

FIGURE 1 is a perspective view of a conventional wood screw before being formed to provide a screw constructed in accordance with the invention;

FIGURE 2 is a perspective view of the same wood screw after being formed in accordance with the invention;

FIGURE 3 shows the screw of FIGURE 2, but turned through 90 about its axis;

FIGURE 4 is an enlarged sectional view taken on line 44 of FIGURE 2;

FIGURE 5 is a perspective view of a wood screw, illustrating a second embodiment of the invention, and

FIGURES 6 and 7 illustrate the operation of a screw according to the invention and show successive positions of the lead end of the screw as it is being driven into a piece of hard wood.

A wood screw having the construction provided by this invention is formed from a conventinal wood, screw, such as that illustrated in FIGURE 1, and which has a shank 2, head 4, pointed lead end 6 and a thread 8 extending from the lead end to a point on the shank removed from the head. The head may be of any known or desired shape or construction and, in FIGURE 1, is shown as a countersunk head of circular cross section having a flat upper surface with a Reed & Prince or Phillips type recess in it. Such a screw causes many and important difficulties when it is driven, or an attempt is made to drive it, into very hard wood.

The invention provides a wood screw which is preferably made from a conventional wood screw such as that shown in FIGURE 1, by modifying it in such a way that it may be driven into very hard wood without splitting the wood or damaging the screw. In accordance with the invention that part of the threaded shank of the screw at and adjacent to its pointed lead end 6 is deformed to provide preferably two spaced, flat, surfaces 20, 22. In the preferred form and practice of the invention these Patented July 24, 1962 surfaces are formed by a stamping or pressing operation exerted laterally of the axis of the screw. This results not only in the formation of the surfaces 20, 22 but also interrupts the thread in the deformed area of the shank and, in addition, by reason of the flow of metal in the pressing or stamping operation, the root diameters at 30, of the interrupted thread remnants which remain between the surfaces 29, 22 are increased above the root diameters of the full, uninterrupted threads at the same area of the shank of the conventional screw shown in FIGURE 1. The root diameters of the interrupted threads at the flattened area of the screw are also greater than the root diameters of the next few convolutions of uninterrupted thread adjacent to the flattened area and removed therefrom in the direction of the head of the screw. Thus, the flattened area of the shank not only has the two fiat surfaces 20, 22 but is also laterally enlarged in the direction parallel to these surfaces and laterally of the axis of the screw. This enlargement of the screw at and adjacent its pointed lead end, and between the flat surfaces 20, 22 is snown at 30 in the drawings.

The upsetting of the metal of the screw by pressing or stamping forces exerted on it, not only increases the root diameters of the interrupted thread remnants, as described, but also causes the formation of very small beads or ridges 40 at each edge of the surfaces 20, 22. These ridges are between the surfaces 20, 22 and the root surfaces 30 and extend along the edges of these surfaces axially of the shank, between the successive interrupted thread remnants.

In the preferred form of the invention which is disclosed in FIGS. 2 to 4, each of the surfaces 20, 22 is made approximately parallel to the normal taper of the remaining uninterrupted threads on its side of the shank, and the two surfaces therefor converge toward the pointed lead end of the screw. Also, in the preferred form of the invention the two flat surfaces are diametrically opposite each other on the shank of the screw.

A typical screw provided by, and in accordance with, my invention would be one which is 1% inches in length, having a head approximately inch in diameter the upper surface of which is cross recessed, as shown in FIGS. 1, 2 and 3, and whose lower surface is of standard countersunk form. The shank of this screw is approximately inch in diameter at its head end and is 1% inches in length, of which approximately inch is threaded from the poined lead end toward the head. The two flat surfaces 20, 22 extend approximately A inch from the pointed lead end of the screw and diverge from the point toward the head at approximately a 15 included angle which is bisected by the axis of the screw. The two flat surfaces are spaced approximately 7 inch apart at maximum divergence. Two complete thread convolutions are interrupted by the flat surfaces and the root diameters of these thread remnants are increased above their dimension in the conventional screw, before deformation in accordance with the invention, and are therefore greater than the root diameters of the next adjacent threads in the direction of the head of the screw, which root diameters are shown at 50 in the drawings. It will be understood that these dimensions are only those of a typical screw constructed in accordance with the invention and are not to be construed in any way as imposing any limitation on the invention.

In a second embodiment of the invention, which is disclosed in FIG. 5 of the drawings, the flat surfaces 60, 62 are formed in the same manner and at the same location as the flat surfaces 26, 22 of the embodiment of themvention disclosed in FIGS. 2 to 4 and described above. However, in this second embodiment of the invention the flat surfaces 60, 62 are substantially parallel to each other and to the axis of the shank. 'In all other respects the structure and operation of this form of the invention are the same as those of the embodiment described above.

FIGURES 6 and 7 of the drawings show the action of the drill point of the screw as the screw is driven into wood without a pre-f-ormed lead hole, and illustrate why the screw will not split the hardest wood, although a conventional screw will do so. As described above, the pressing or stamping operation to which the pointed lead end of the shank is subjected to form the flat surfaces 20, 22 or 60, 62 causes enlargement of the shank in a direction normal to the direction of the pressing or stamping, this enlargement being illustrated at 30 in the drawings. As stated above, the root diameter of the interrupted thread remnants between the flat surfaces are greater than those of the threads at the same location of a conventional wood screw of the same dimensions, and are also greater than the root diameter, of the next adjacent un-interrupted threads in the direction of the head of the screw. Therefore, as the screw is driven into the wood the enlarged, flattened part adjacent the pointed lead end of th screw, which part is defined by the flat surfaces 20, 22 or 60, 62 the enlarged root parts 30, and which part has sharp edges between the interrupted thread remnants, acts as a chisel or gouge to cut out the wood, forming a clearance for the root of the thread in advance of the main part of th length of the threaded shank. This action causes an opening 70 to be formed at the lead end of the screw in every position of the lead end as it is driven into the wood, and the succeeding thread convolutions 8 move into this opening as the screw advances into the wood, thus relieving the pressure of the screw on the wood and preventing splitting. The enlargement, at 30, of the flattened part of the screw is sufficient to perform the function described above, but is not sufficient to produce an opening of such large diameter that the thread 8 will not have secure engagement with the wood.

The drill point of the screw, comprising the flat surfaces and enlarged thread remnants, both displaces and pulverizes wood as the screw is being driven. During the first part of the entry of the screw into the wood a small quantity of pulverized wood forms on the surface of the wood around the screw, being passed back to the surface by the turning helix of the thread. As the shank of the screw moves further into the wood all of the pulverized wood remains in the hole. During this later movement of the screw the drill point, at which the interrupted thread remnants have greater root diameters than the following thread convolutions, forms a hole having greater diameter than that of the shank at the following thread convolutions and, as the shank of the following convolutions moves into the hole formed by the drill point, the pulverized wood removed by the drill point lodges in the cylindrical recess between the shank of the following convolutions and the wall of the enlarged hole formed by the drill point. This disposition of the wood removed by the drill point is indicated by the fact that as the screw advances into the wood after its initial entry no pulverized wood appears on the surface of the wood around the screw.

In the foregoing specification and in the accompanying drawings the invention is described and illustrated as comprising, among other things, two flat surfaces which are formed by stamping or pressing. The invention is not limited to a screw having two such surfaces and, further, is not limited to the formation of such surface or surfaces by stamping or pressing or by any specific metal working operation. However, in the preferred form of the invention there are two surfaces formed by stamping or pressing.

Further, other embodiments of the invention in addition to those disclosed, as well as modifications of the disclosed embodiments, may be made and practised without departing in any way from the spirit or scope of the l invention, for the limits of which reference must be made to the appended claims.

What is claimed is:

1. A wood screw comprising a shank having a head at one end and being pointed at the other end and having a raised helical thread thereon extending from the pointed end toward the head, the convolutions of which are spaced apart to define a flat root portion therebetween, the shank and thread having at least one flat surface adjacent to the pointed end thereof which extends entirely across the shank as a chord thereof and which. interrupts the thread leaving thread remnants, the root diameter of the interrupted thread remnant next to the first full thread convolution adjacent the interrupted thread remnants in the direction of the head being enlarged radially of the shank and having a root diameter which is greater than that of said first full thread convolution and which is less than that of the thread adjacent the head, the line of intersection of each edge of the flat surface with the edge of the root portion of the enlarged interrupted thread remnant forming a cutting edge having a defined longitudinal extent.

2. A wood screw comprising a shank having a head at one end and being pointed at the other end and having a raised helical thread thereon extending from the pointed end toward the head, the convolutions of which are spaced apart to define a fiat root portion therebetween, the shank having two flat surfaces adjacent the pointed end thereof both of which extend entirely across the shank as chords thereof and which interrupt the thread leaving thread remnants therebetween, the root diameter of the interrupted thread remnants next to the first full thread convolution adjacent the interrupted thread remnants in the direction of the head being enlarged radially of the shank and having a root diameter which is greater than that of said first full thread convolution and which is less than that of the thread adjacent the head, the line of intersection of each edge of each fiat surface with the edge of the root portion of each enlarged interrupted thread remnant forming a cutting edge having a defined longitudinal extent.

3. A wood screw comprising a shank having a head at one end and being pointed at the other end and having a raised helical thread thereon extending from the pointed end toward the head, the convolutions of which are spaced apart to define a flat root portion therebetween, the shank having two substantially parallel flat surfaces adjacent the pointed end thereof both of which extend entirely across the shank as chords thereof and which interrupt the thread leaving thread remnants therebetween, the root diameter of the interrupted thread remnants next to the first full thread convolution adjacent the interrupted thread remnants in the direction of the head being enlarged radially of the shank and having a root diameter which is greater than that of said first full thread convolution and which is less than that of the thread adjacent the head, the line of intersection of each edge of each fiat surface with the edge of the root portion of each enlarged interrupted thread remnant forming a cutting edge having a defined longitudinal extent.

References Cited in the file of this patent UNITED STATES PATENTS 143,217 Barrett Sept. 30, 1873 684,774 Baggs Oct. 22, 1901 2,403,359 Gerhold July 2, 1946 2,507,882 Berman May 16, 1950 2,654,284 Schevenell Oct. 6, 1953 2,871,752 Stern Feb. 3, 1959 2,959,086 Gerlach et al Nov. 8, 1960 FOREIGN PATENTS 167,620 Great Britain Aug. 18, 1921 690,269 Great Britain Apr. 15, 1953 

